Poster X20 - Alumina-coated microparticles enable extended dosing of HIV Env antigens from a single injection

Introduction: Current prophylactic approaches against HIV focus on triggering B-cells with the capability to produce high-affinity broadly neutralizing antibodies (bnAbs). Engaging the rare precursor B-cells capable of becoming bnAb producers is greatly enhanced by “extended dosing” vaccination regimens that employ repeated antigen injections to prolong antigen exposure during priming. However, such regimens are impractical for global vaccination campaigns. Novel controlled-release technologies that can mimic extended dosing regimens in a single-injection formulation may overcome barriers impeding vaccine success. Here, we developed an extended-dose delivery system by encapsulating a stabilized SOSIP-based HIV Env trimer and a saponin MPLA nanoparticle (SMNP) adjuvant inside alumina-coated trehalose microparticles using atomic layer deposition (ALD). Vaccine release kinetics were modulated by controlling the thickness of the alumina coat on the sugar-glass microparticles. We anticipate that this platform will deliver multi-dose regimens in a single dose, easing global vaccination.

Materials and

Methods: Env trimer was expressed in Expi 293F cells and purified by affinity chromatography using a GE HisTrap column and size-exclusion chromatography using a GE S200 Increase column. SMNP was prepared by mixing Quil-A:cholesterol:DPPC:MPLA at a molar ratio of 10:10:2.5:1 in 20% w/v MEGA-10 followed by dilution with PBS to a final concentration of 1 mg/ml cholesterol. The solution was allowed to equilibrate overnight at room temperature, followed by dialysis against PBS using a 10k MWCO cassette. SMNP was further purified using a Sephacryl S-500 HR size exclusion column. Next, the trimer and SMNP were formulated in histidine HCl, endotoxin-free trehalose, hydroxyethyl starch, NaCl, and Tween 80 and spray dried in a Buchi B-290 Mini Spray Dryer. Water content was measured by Karl-Fischer titration. Spray dried powder and zirconia beads were loaded into a custom fluidized bed reactor and purged with argon. The powder was alternately fluidized with trimethyl aluminum and water vapors to deposit 0.2 nm alumina per cycle on the particles.

Results, Conclusions, and Discussions: Antigenicity profiling of the trimer using a panel of neutralizing and non-neutralizing antibodies showed the protein to be structurally intact inside the ALD microparticles. In mice, ALD particles delayed immunogen release and antibody responses in a coating thickness-dependent manner. Further, extended-dose regimens recapitulated using ALD particles showed significantly higher antibody responses compared to bolus immunization. These results show that ALD-coated microparticles can successfully deliver extended dose regimens in a single-dose formulation, which may ease vaccination efforts.

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